In the manufacture of glass, such as E glass fibers or filaments, by a continuous melting process, glass batch material is delivered to a furnace at the upstream end of the melting and refining tank. The glass batch material is melted and refined as it passes through the melting and refining tank to a forehearth which is connected to the downstream end of the melting and refining tank. The glass is withdrawn from the melting and refining tank into a conditioning section of the forehearth from which the glass passes to the working forehearth where the glass is distributed to fiber forming equipment and withdrawn from the forehearth through the fiber forming equipment to form the fibers or filaments.
In conventional E glass furnaces of the type shown in FIG. 1, the glass batch materials are melted by directly opposed air/gas fired burners which extend for substantially the entire length of the melting and refining tank. The forehearth is also fired with directly opposed air/gas burners to further refine the glass and to regulate and maintain the glass at the desired temperature for the fiber or filament forming process.
In a typical combustion process using an air/gas fired burner, natural gas and air is usually combined in a set ratio of 10 parts air to 1 part natural gas by volume. The main drawback to this method of combustion is the nitrogen content of air which constitutes 78% of air by volume and contributes nothing to the combustion process. Thus with air/gas fired burners, large volumes of air are required relative the volume of natural gas consumed. The relatively large volumes of combustion air and the resulting large volumes of exhaust gases which must be processed using air/gas fired burners require the use of costly, high volume combustion air and exhaust gas systems.
For more efficient combustion, the air supplied to the air/gas fired burners should be preheated from ambient temperatures to temperatures of about 1200 degrees Fahrenheit. Since the volume of air to natural gas employed by the burners is approximately 10 to 1, relatively large volumes of air must be heated to these high temperatures and delivered to the burners for use in the process. This requires the use of high temperature metal recuperators to preheat the combustion air and high temperature metal piping and insulation to deliver the hot air to the burners. These recuperators are expensive to construct and, with the highly corrosive exhaust gases that pass through them, costly to maintain.
In addition to greatly increasing the volume of gases to be preheated and handled in the combustion system, the presence of nitrogen in the air detracts from the heating process by carrying part of the heat of combustion away from the process. Thus, part of the heat of combustion goes to the nitrogen rather than to the glass melt for which it is intended and contributes nothing to the process. The presence of nitrogen in the combustion process also leads to the formation of nitrogen oxide emissions.
The low efficiencies of the air/gas fired burners require the use of a large number of burners along substantially the entire length of the melting and refining tank in order to melt and refine the glass batch materials. The furnace illustrated in FIG. 1 uses a total of thirty-two air/gas fired burners in the melting and refining tank.